In the area of the beverage industry in particular, plastic bottles have for a long time been used in addition to glass bottles for bottled beverages. In the production of these plastic bottles, a plastic blank, also called a parison or preform, may be heated, placed in a blow mold and then blow molded to its final size. This is usually done by using blow molds, which are closed around the outside of the blank to be blow molded, and then compressed air is injected through the opening in the mold.
The mouthpiece of the future bottle is already completed on the parison and is not processed further. For the actual blowing operation, a circumferential edge or collar of the parison rests on a circumferential edge of the blow mold, thus preventing the parison from collapsing into the interior of the blow mold.
In other words, as soon as the blow mold is closed, the parison, i.e., the so-called perform, lies directly on a plane of the blow mold and/or a ring, which is also referred to as the neck plate, before the stretch blow molding operation.
A spring-loaded grip is generally used for feeding the parison into the blow mold. Following this, the mold is closed and then the spring-loaded grip is tightened. In this stage of production, the preform may become tilted slightly in the blow mold because a mold gap must be maintained between the preform and the blow mold at this point. This mold gap is necessary to ensure clean closing of the blow mold. The size of this gap between the preform and the blow mold is usually between 0.25 mm and 0.4 mm.
When there are large mold gaps in particular, it may happen that a one-sided contact with the inside wall of the blow mold occurs with the above-mentioned slight tilting of the preform when the grip is removed. At this contact point, the hot preform cools slightly, but after the blow molding operation, this contact may result in the bottle having a one-sided accumulation of material, which is also known as a quenching lens, beneath the supporting ring.
Therefore, the object of the present disclosure is to rule out or at least reduce the risk of development of such a quenching lens. The inventive blow mold for producing plastic containers has a base body, which is preferably closable; the body of the container to be produced can be held in the interior of this base body; the inside wall of this base body, in particular in the closed state, completely surrounds the body of the container to be held. The blow mold here has a circumferential edge for supporting the neck of the container with respect to the blow mold.
According to the present disclosure, a spacer device that protrudes toward the inside with respect to the blow mold and/or the circumferential edge is provided on the circumferential edge, preventing the body of the container from coming in contact with the inside wall of the blow mold in the event the container becomes tilted with respect to the blow mold.
The circumferential edge of the blow mold may be designed in one piece with the blow mold but the circumferential edge is preferably part of a ring on which the bottle, i.e., the preform, rests during the blowing operation. More precisely, the collar or a circumferential edge of the bottle rests on this circumferential edge. Support of the container with respect to the blow mold is understood in particular to refer to the fact that before the blowing operation, the container and the blow mold are in contact only at said collar of the container and preferably there are no other points of contact between the container and the inside wall of the blow mold.
The spacer device is preferably designed in one piece with the ring and protrudes inward with respect to an opening formed by the ring.
The spacer device is preferably designed in the form of a ring, such that it completely surrounds a section of the container. This ring-shaped spacer device is designed especially preferably in one piece with the ring. In addition, however, it would also be conceivable for the spacer device to have a plurality of protrusions extending radially inward with respect to the blow mold and/or the ring and extending in the direction of the longitudinal axis of the container. The diameter of the opening formed by the ring is thus reduced by the spacer device.
The spacer device is preferably flush with the circumferential edge upwardly. This means that the spacer device protrudes up out of the circumferential edge and/or the ring and thus the collar of the container with its underside do not come in contact with this spacer device at all or do not come in contact with it exclusively. In addition, the spacer device in this embodiment is connected directly to the circumferential edge toward the bottom. This will be explained in greater detail below with reference to the figures.
In another embodiment, the spacer device has a rectangular cross section in its circumferential direction. Although, as mentioned above, the spacer device is designed as a ring, this ring in turn has said rectangular cross-section in its circumferential direction. In particular, the transition between the spacer device and the centering ring and/or the blow mold is selected to be sharp-edged and without a burr.
The spacer device 10 preferably has a length of between 0.5 mm and 8 mm, preferably between 1 mm and 4 mm and more preferably between 1.5 mm and 3 mm in the longitudinal direction of the container 4. A length in the range of 2 mm has proven to be especially advantageous to prevent tilting of the container and thus the quenching lenses mentioned above, while on the other hand not having an excessively negative effect on the container production process. In other words, by narrowing this area beneath the collar of the container, the tilt angle is reduced. In addition, this also achieves the result that the mold contact occurs in the (immediate) vicinity of the supporting ring and/or the area in which the collar of the container is supported. This is not problematical because the plastic material is still cold in these areas and thus not participate in the stretch blow molding operation.
The disclosure narrowing of the area beneath the collar and/or the spacer device is advantageous in particular with such blow molds that produce a steep bottleneck such as that on a contoured bottle, for example.
Both the circumferential edge and the spacer device on the ring mentioned above are thus advantageously arranged there.
The present disclosure is also directed at a ring for a blow mold of the type described above such that this ring has a planar circumferential edge on which may be supported a collar of a container that is to be processed and in particular is to be blow molded.
In addition, a cylindrical section is provided, extending essentially perpendicular to the plane of the circumferential edge. A spacer device extending radially inward with regard to this cylindrical section is provided on this cylindrical section according to this disclosure. This spacer device preferably has a circular cross section.